2020 BUILDING INFORMATION MODELING (BIM) AWARD AND CUSTOM SOLUTION HONORABLE MENTION Key Project attributes ❚ Precasters used BIM to achieve near zero tolerances on the complex curved structure. ❚ Precast concrete accelerated erection and will be resilient in the harsh climate. ❚ The structure is self-supporting and does not have bracing, finishes, or other nonessential additions. TOWER OF VOICES– FLIGHT 93 MEMORIAL STOYSTOWN, PENNSYLVANIA The Tower of Voices National Memorial in Stoystown, Pa., is as much a musical instrument as it is a monument. The 93-ft-tall precast concrete tower houses 40 custom-made aluminum wind chimes. Each chime was cast to produce a distinct musical note, so that together they create a set of 40 “voices” to memorialize the 40 passengers and crew who lost their lives when United Airlines Flight 93 was hijacked by terrorists on September 11, 2001. Precast concrete was selected for the tower frame because of the precision required to accommodate the complex and unusual shapes of each component and the strength needed to support the tall, slender frame, says Paul Murdoch of Paul Murdoch Architects. “The customizable nature of precast concrete allowed for a unique design, featuring faceted columns and diagonal, curved beams.” Project and Precast concrete scoPe ❚ Create a 93-ft-tall precast concrete memorial featuring 40 custom wind chimes to represent the voices of the 40 passengers of United Airlines Flight 93. ❚ The project features 58 precast concrete elements, including 36 beams angled to represent surrounding trees. ❚ The project was completed in 12 months, with precast concrete erection completed in two months. BIM ACCOMMODATES ZERO TOLERANCE The 93-ft-tall tower features a cross section in a “C” shape that allows sound to reflect outward from the open side in a fan-shaped pattern. The chimes are sus-pended at various heights within the tower, starting from 20 ft above the main plaza and ascending to the top. The elegant design is a beautiful memorial to the people aboard Flight 93; how-ever, it created some construction challenges. The structure lacked a clean geo-metric starting point due to its curves, and this made form building and checking the pieces extremely difficult, says Greg Gorman, senior vice president and chief operating officer for PennStress. The design also required an extremely high degree of accuracy. “The use of building information modeling (BIM) software was imperative to ensure that the detailed geometry of the pieces was exact, and that no interferences for the re-inforcing steel, splice sleeves, lifters, electrical conduit, or various other internal components could occur,” Gorman says. His team used three-dimensional printing technology to create prototypes to better understand the structural relationships between the tower columns and beams. “The pieces were designed in a circular and skewed layout, adding com-plexity that required a BIM program to ensure accuracy,” Gorman says. Several scale mock-ups were also created and collaboratively discussed to ensure the best possible connections. This ensured not only that the structure looked as it should but also that it would maintain its appearance after the precast concrete was coated with a water-repellent coating and anti-graffiti protection. During the design phase, the precast concrete producer determined that the slenderness of the full-length columns would make them too vulnerable to dam-age during transportation and erection. Therefore, PennStress used diagonal col-umn splices that allowed the joints to blend in with the diagonal beams. “The precast concrete structure provides a long-term monument with an everlasting look as a tribute to the brave men and women of Flight 93.” — Paul Murdoch, Paul Murdoch Architects
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